The deep sea is in trouble. A recent study has found that it's being damaged by human activities, and that this is only likely to get worse. Scientists are now calling for better management and conservation of entire deep-sea ecosystems.

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It's so 'out of sight, out of mind' that people have used the deep sea as a dumping ground for hundreds of years. While this is still a problem, the report's authors say that the deep sea's most pressing threat now comes from exploitation and the effects of climate change.

The deep sea — classed as waters deeper than 200 metres — covers 360 million square kilometres and makes up around half of the Earth's surface, making it the largest environment and last great wilderness on Earth. Depths average nearly four kilometres, but reach almost 11 kilometres at the deepest trench on Earth, the Marianas Trench.

It's an understudied, alien world. But far from being devoid of life, it's teeming with unusual creatures that can survive the darkness and immense pressures. It's also full of valuable resources: fish, minerals, and — under the seafloor — oil and gas. This makes it particularly prone to exploitation.

But how exactly do our activities affect the deep sea?

'It's a difficult question to answer, because we know comparatively little about it,' says Professor Paul Tyler from the National Oceanography Centre, Southampton, co-author of the study, published in PLoS One this month. 'But during scientific trawls back in the 80s, it wasn't uncommon to bring up oil drums, and that's just in one small area.'